This invention relates to a fastening device which provides secure, vibration-resistant electrical coupling to a printed circuit board. More specifically, the invention relates to a fastening device which rigidly secures a printed circuit board having electrically conductive fingers extending from the edge to a circuit board edge connector which electrically couples with the fingers.
Printed circuit boards generally comprise a sheet of insulative material onto which electrically conductive material is deposited. Electrical coupling to the circuit board is provided by a plurality of electrically conductive fingers which extend outward from the edge of the circuit board. The most basic and least expensive type of edge connector is one having a plurality of finger receiving slots defined by electrically conductive contact, and a plurality of outward-extending electrical leads connected to the contacts. This edge connector permits the printed circuit board to be electrically coupled with external electrical devices or circuits. One such type of simple edge connector is TRW Cinch Model 252-22-90-210.
In most cases the electrical leads which extend outward from the back of the edge connector are individually connected to separate electrical wires. However, the electrical leads on the edge connector are also capable of being directly coupled to a second printed circuit board. In such a construction the electrical leads extend through holes in the plane of the second circuit board and are soldered to the printed circuits deposited on the second connector board. The finger receiving slots of the edge connector used in such an electrical circuit construction thus extend normal from the plane of the second circuit board, and are coupled with the fingers of the first circuit board. The result of such a construction is two mutually perpendicular electrically coupled circuit boards.
In order to prevent the edge connector from becoming detached from the circuit board or to prevent mutually perpendicular circuit boards from becoming disconnected, it is desirable to rigidly secure the edge connector to the printed circuit board. This rigid securing is required not only when two circuit boards are connected to one another in the mutually perpendicular fashion, but also when a single circuit board is coupled with a single edge connector. Such securing is required primarily in situations where the circuit boards may be subjected to vibration.
In many applications a printed circuit board is secured to the edge connector only by the spring-like gripping forces applied to the fingers of the circuit board by the electrically conductive contacts which define the slots of the edge connector. In one such application the boards are inserted in a housing or cabinet and aligned in mutually perpendicularly spaced parallel planes with each of the circuit boards having its electrically conductive fingers oriented in the same direction. The edge connectors for the circuit boards are attached to a hinged locking plate which moves the edge connectors into locked engagement with the fingers of the circuit boards. In other applications, each edge connector is simply manually engaged with the conductive fingers of the circuit board.
This latter application has the inherent disadvantage that electrical contact between the circuit and the edge connector is likely to be impaired or lost when the board and edge connector are subjected to mechanical vibration.
There are more elaborate and costly edge connectors available which have gripping means, such as spring clips, for securing the edge connector to the circuit board and thus preventing disruption or loss of electrical contact during vibration. However, there are no commercially available fastening devices which rigidly secure the basic and inexpensive type of edge connector to a single printed circuit board. When such rigid securing is desired, it is often necessary to fabricate a fastening member and to attach the member to the circuit board by a bolt and nut. This practice requires the use of insulative washers since the bolt head and the nut are electrically conductive and would otherwise interfere with the circuits printed on the board. Additionally, the assembly of nuts and bolts on each circuit board is time consuming and thus expensive, especially when a large number of circuit boards and the edge connectors are to be secured.